The disclosure of Japanese Patent Application No. 2000-183516 is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a torque converter and, in particular, to a thrust force supporting structure of a stator thereof.
2. Description of Related Art
A torque converter is generally configured to have a stator interposed between a pump impeller and a turbine runner. The stator is radially supported on an appropriate fixed member, through an annular one-way clutch, in such a manner that the stator is rotatable in one direction. At the same time, the stator is axially supported between the pump impeller and the turbine runner (in particular, its hub) through annular thrust bearings. Conventionally, the diameters of the one-way clutch and the thrust bearings for supporting the stator are substantially the same. In addition, the one-way clutch and the thrust bearings are arranged to axially overlap one another such that the one-way clutch is interposed between thrust bearings (See Japanese Patent Laid-Open Publication No.HEI8-14382 as an example).
As mentioned above, in a conventional torque converter, a one-way clutch and a pair of thrust bearings are axially arranged in substantially the same radial position in the area radially inside of a stator. This arrangement creates a long axial length of an inner area of a torque converter, and thus prevents the axial length of a torque converter from becoming shorter. In addition, since thrust bearings overlap side bearings of the one-way clutch, the thrust force is transmitted between the thrust bearings and an outer race of the one-way clutch through the side bearings of the one-way clutch. Therefore, the side bearings should be thick enough to bear this thrust force. Furthermore, side bearings need to have a complicated shape to transmit a thrust force between the thrust bearings and the outer race of the one-way clutch, which are arranged in different radial positions.
Also, automatic transmissions for automotive vehicles are becoming multi-speed types, and accordingly, the transmission mechanism is becoming complicated. Under these circumstances, it is necessary to prevent the axial length of the transmissions from becoming longer due to the increase in the complexity of the transmission mechanism. Thus, there is a strong need for shortening the axial length of a torque converter for an automatic transmission, especially for front engine front drive or a rear engine rear drive vehicles in which an automatic transmission and an engine are transversally arranged in an axial direction within the width of the tread.
Accordingly, the invention provides a torque converter wherein an axial length of the area radially inside of a stator is shortened by improving the arrangement of a one-way clutch and thrust bearings.
To achieve this, a torque converter, according to a first exemplary aspect of the invention, comprises a one-way clutch for supporting a stator radially on a fixed member in such a manner that the stator is rotatable in one direction, and thrust bearings for supporting the stator axially between a pump impeller and a turbine runner, characterized in that the diameters of the one-way clutch and the thrust bearings are different, and the thrust bearings do not axially overlap at least side bearings of the one-way clutch. In the above configuration, since a thrust force is transmitted between the stator and the thrust bearings without the intermediation of the side bearings of the one-way clutch, the thrust load is not applied to the side bearings and the side bearings are made thinner than conventional side bearings. Thus, the axial length of the area radially inside of the stator in the torque converter can be shortened. Also, because the thrust force does not need to be transmitted, the shape of the side bearings can be simplified.
In an embodiment of the first exemplary aspect of the invention, at least a portion of the thrust bearings is arranged to radially overlap the one-way clutch. Therefore, the axial length of the area for arranging the one-way clutch and the thrust bearings can be shortened by the axial length of the radially overlapping portion. Thus, the axial length of the area radially inside of the stator can be shortened even further.
In another embodiment of the first exemplary aspect of the invention, the thrust bearings are arranged radially outside of the one-way clutch. Therefore, it becomes possible to improve durability of the thrust bearings by enlarging the diameter of the thrust bearings, for which securing durability is usually more difficult than for a one-way clutch of the same diameter.
In a further embodiment of the first exemplary aspect of the invention, oil passages forming a communicative connection between radially outside and inside of the thrust bearings are provided on a supporting surface of a member abutting to the thrust bearings. Therefore, since it is possible to provide oil passages required for supplying and exhausting hydraulic oil to and from a truss portion of the torque converter without providing oil passages in the side bearings, the shape of the side bearings can be simplified, thereby reducing the manufacturing costs.